The first, or primary stage of conventional liquid born waste treatment, as currently practiced, consists of sedimentation of heavy inorganic detritus called grit, followed by floatation of light materials called floatables and congealed fat called grease, and sedimentation of heavier organic solids called sludge. Grit is generally disposed of by burial on a day by day basis. Sludge is usually taken off in a side stream and treated in a separate sludge digester where its organic content is partially converted to carbon dioxide, methane, and inert gases, and the residue is de-watered and disposed of, usually by burial. Floatable material along with grease is either finely ground and introduced to a separate sludge digester with sludge or disposed of separately by burial or incineration. Under new pollution control legislation, grit, floatable materials and fresh or partially stabilized sewage sludge, unless heat treated or heavily disinfected with chlorine, are regarded as highly infectious and potentially toxic or hazardous. Thus, to handle and dispose of them safely is extremely expensive.
In view of the foregoing, it would be highly desirable to provide an improved technique for wastewater treatment. Ideally, the system would be low cost and would not require frequent waste handling.